1. Field of the Invention
The present invention relates to an electrode rod for detecting water-level attached to a metal container and used for detecting water-level in the container, to a method of detecting water-level employing the electrode rod for detecting water-level, to a method of controlling water-level in a boiler, and to a method of controlling water-level in a steam separator.
2. Description of the Related Art
A vapor to be generated in a boiler is mixed with water in a state where bubbles generated in a water tube of the boiler exceed an upper header under heating, and the vapor to be obtained becomes a bad quality wet vapor with much moisture. In the case where the bubbles generated in the water tube do not reach the upper header, water is not mixed with the generated vapor, and the vapor to be obtained becomes a good quality dry vapor. However, the case where a position of the bubbles generated in the water tube is low and a water film of bubbles cannot be formed in the upper header leads to a situation where the upper header is overheated by flame, melted, and damaged because the water tube is produced from iron. Thus, water-level in the water tube must be controlled to water-level such that the bubbles generated in the water tube do not exceed the upper header under heating and the water film is formed in the upper header.
The water-level in the water tube is determined by size of the bubbles to be generated under heating. That is, in the case where the bubbles to be generated are large, the water-level is lowered, and in the case where the bubbles to be generated are small, the water-level is raised. The size of the bubbles to be generated varies depending on burning capacity, vapor pressure, supply water temperature, electrical conductivity of boiler water, and the like during operation of the boiler.
Thus, in the boiler, the water-level in the water tube is controlled by: setting optimum water-level in accordance with the burning capacity, vapor pressure, supply water temperature, electrical conductivity of boiler water, and the like; detecting the water-level in the water tube with an electrode rod for detecting water-level; and supplying water or stopping water supply to the water tube so as to adjust the water-level to water-level in accordance with the burning capacity, vapor pressure, supply water temperature, electrical conductivity of boiler water, and the like during operation of the boiler.
In a conventional boiler, detection of the water-level in the water tube with the electrode rod for detecting water-level is carried out as described below.
The electrode rod for detecting water-level is provided with an external power supply connecting terminal part to be connected to a power supply, and a water-level detecting electrode part to be brought into contact with water, and is attached to a metal container for detecting water-level communicating with a water tube of a boiler through an insulator. The container communicating with the water tube of the boiler holds water common with that of the water tube of the boiler, and the held water has water-level common with the water-level in the water tube. One side of the power supply is connected to the external power supply connecting terminal part of the electrode rod for detecting water-level, and another side of the power supply is connected to the container for energization. Whether the water-level has reached the water-level detecting electrode part can be detected by change in conduction state between the external power supply connecting terminal part and the container.
The container is provided with a plurality of electrode rods for detecting water-level of different lengths corresponding to water-level set based on the burning capacity, vapor pressure, supply water temperature, and electrical conductivity of boiler water. The water-level in the container detected by each electrode rod for detecting water-level is sent to a water-level controlling device. Water supply is controlled so that there is provided water-level set in accordance with the burning capacity, vapor pressure, supply water temperature, electrical conductivity of boiler water, and the like during operation of the boiler, and the water-level in the water tube is controlled to predetermined water-level (see JP 06-147407 A, for example).
Meanwhile, in the boiler, a vapor generated under heating of the water tube is taken out from the upper header to be sent a loading side, but the vapor taken out from the upper header contains boiler water, and the vapor containing the boiler water is a bad quality wet vapor with much moisture.
Thus, the boiler is generally provided with a steam separator for separating moisture from the vapor taken out from the upper header. The case where water-level in the steam separator is too high involves situations in that the generated vapor easily contains boiler water and dryness of the vapor reduces. In contrast, in the case where the water-level in the steam separator is too low, an ability of the steam separator is sufficiently exerted and a good quality dry vapor is obtained. However, the water-level in the water tube may be low. The case where the water-level in the water tube is low involves situations in that the position of the bubbles generated in the water tube is low and a water film of bubbles cannot be formed in the upper header. Thus, this case may involve a situation in that an upper part of the water tube and the upper header are overheated by flame, melted, and damaged because the water tube is produced from iron.
For avoiding such situations, the water-level in the steam separator is controlled to a certain level for controlling the water-level in the water tube such that increase in an amount of boiler water to be mixed with the generated vapor is restricted and the water film is formed in the upper header.
As means of controlling the water-level in the steam separator to a certain level, there is known a control method involving detecting water-level in a steam separator with an electrode rod for detecting water-level and turning on and off a water supply pump for supplying boiler water to a water tube in accordance with the detected water-level. The method of controlling water-level in a steam separator involves: setting upper limit water-level and lower limit water-level for the water-level in the steam separator; and turning off the water supply pump when the upper limit water-level is detected and turning on the water supply pump when the lower limit water-level is detected for constantly maintaining the water-level in the steam separator between the upper limit water-level and the lower limit water-level (see JP 2003-294204 A, for example).
The electrode rod for detecting water-level to be used for detecting the water-level in a conventional steam separator has the same structure as the electrode rod for detecting water-level to be used for detecting the water-level in the water tube of the boiler. Detection of the water-level is carried out as described below.
The electrode rod for detecting water-level is attached to a metal container for detecting water-level in a steam separator communicating with the steam separator through an insulator. The container holds water common with that of the water tube of the steam separator, and the held water has water-level common with the water-level in the steam separator. One side of the power supply is connected to the external power supply connecting terminal part of the electrode rod for detecting water-level, and another side of the power supply is connected to the container for energization. Whether the water-level has reached the water-level detecting electrode part can be detected by change in conduction state between the external power supply connecting terminal part and the container.